1. Field of the Invention
This invention relates, primarily, to composite expansion joint materials for high temperature service, i.e., conditions where gas temperatures exceed 600xc2x0 F.
2. Description of the Prior Art
Early examples of high temperature composite expansion joint materials are described in U.S. Pat. Nos. 5,296,287 and 5,496,628 (Ribbans), the disclosures of which are herein incorporated by reference. Such materials typically comprise a non-fluoropolymer thermal barrier (woven fiberglass mat) laminated to a fluid barrier (fluoropolymer film) and/or a load bearing composite (fluoropolymer coated fiberglass fabric). Lamination is typically effected by melt bondable adhesives, e.g. PFA, FEP, MFA, etc.
Although the performance of such products was excellent, their widespread acceptance by the industry was somewhat hampered by their high costs, due in part part to the high cost of the woven fiberglass mats used as the thermal barrier components.
Equally efficient and far less expensive nonwoven xe2x80x9cneedledxe2x80x9d fiberglass mats were available, but their use was discounted due to the then perceived difficulty of effectively coating such high porosity materials with melt bondable adhesives. The adhesives would simply xe2x80x9cwickxe2x80x9d into the needled mats, with insufficient adhesive remaining at the lamination interface to effect an adequate bond with the mating component.
This problem was eventually solved by the introduction of the so call xe2x80x9cglue sheetxe2x80x9d, an adhesive coated carrier element of the type described in U.S. Pat. No. 5,368,923 (Tippett), the disclosure of which is herein incorporated by reference. The adhesive carrier sheet comprised a light weight scrim coated with the melt bondable adhesive, typically PFA. During lamination, the adhesive remained locally confined at the lamination interface, resulting in an effective bonding without adhesive loss through wicking into the porous needled mat. Although highly successful in this regard, the relatively high cost of the adhesive carrier sheet continued to be a drawback.
Accordingly, the objective of the present invention is to overcome the above described problems and associated drawbacks by providing an improved lower cost high temperature composite expansion joint material in which the needled fiberglass mat is bonded to a fluid barrier component and/or a load bearing component by a surface coating of a fluoropolymer based dispersion. The surface coating is selectively applied to a depth which is less than the overall mat thickness, thereby efficiently conserving adhesive material while avoiding excessive penetration and resulting unwanted stiffness.
A companion objective of the present invention is to improve the resulting bond while further restricting adhesive penetration by densifying the needled fiberglass mat as a preparatory step to lamination with the other components of the composite.
A single membrane insulation material including a nonwoven insulation mat, a fluoropolymer based dispersion surface coated onto one side of the mat and a fluoropolymer containing component laminated to the thus coated side of the mat under conditions of elevated temperature and pressure. The coating has a depth of penetration which is less than the total thickness of the mat.
These and other objects, features and advantages of the present invention will hereinafter be described in greater detail with reference to the accompanying drawings, wherein: